Nutrient Management Research Database

https://www.researchgate.net/publication/236837030_Quantifying_the_Effects_of_Green_Waste_Compost_Application_Water_Content_and_Nitrogen_Fertilization_on_Nitrous_Oxide_Emissions_in_10_Agricultural_Soils

Common management practices, such as the application of
green waste compost, soil moisture manipulation, and nitrogen
fertilization, affect nitrous oxide (N2O) emissions from agricultural
soils. To expand our understanding of how soils interact with these
controls, we studied their effects in 10 agricultural soils. Application
of compost slightly increased N2O emissions in soils with low initial
levels of inorganic N and low background emission. For soils in
which compost caused a decrease in emission, this decrease was
larger than any of the observed increases in the other soils. The five
most important factors driving emission across all soils, in order
of increasing importance, were native dissolved organic carbon
(DOC), treatment-induced change in DOC, native inorganic N,
change in pH, and soil iron (Fe). Notable was the prominence of
Fe as a regulator of N2O emission. In general, compost is a viable
amendment, considering the agronomic benefits it provides against
the risk of producing a small increase in N2O emissions. However, if
soil properties and conditions are taken into account, management
can recognize the potential effect of compost and thereby reduce
N2O emissions from susceptible soils, particularly by avoiding
application of compost under wet conditions and together with
ammonium fertilizer.

• Soil samples (top 15cm) were collected from 10 agricultural fields representing a diverse range of soils from the main agricultural production areas of California.
• Soil samples were collected before fertilizer application.
• Compost samples were collected from yard green waste compost windrows (composted more than 8 weeks and met the mandated Process to Further Reduce Pathogens requirement for soil application).
• Sampled soil was mixed with dry mass of ground compost and incubated in jars at 40% water holding capacity (to simulate field conditions) for 7 days.
• Controls with no compost were incubated under the same conditions.
• Each soil compost/ noncompost jar received 3 fertilization treatments (Ammonium Sulfate, Potassium Nitrate, and no fertilizer)
• The treatments were incubated for 14 days at 22 degrees Celsius (71.6 degrees Fahrenheit)
• Gas samples for Nitrous Oxide were taken from the treatment on Days 0, 1, 2, 3, 5, 9, and 14.
• Gas samples were analyzed using a gas chromatograph.
• After incubation, soils were extracted and analyzed for basic soil parameters including: dissolved organic carbon, pH, total carbon and nitrogen, soil texture, and Iron concentration.
• Statistical Analysis was carried out on collected data in order to identify the most important drivers of Nitrous Oxide emissions while accounting for variability across soils.

• Compost application promoted N₂O emissions in soils which had low initial inorganic nitrogen and low background N₂O emissions.
• Decreased N₂O emissions by compost application occurred in other soils, and this decrease was significantly larger than N₂O emission increases mentioned above.
• The application of compost increased soil organic carbon availability.
• The application of compost increased dissolved organic carbon and inorganic nitrogen, however inorganic nitrogen levels were found to decrease during the period of incubation (more so than the noncompost control).
• Increase in soil moisture resulted in increase in N₂O emissions across all soils.
• Type of fertilizer was also an important factor: Soils fertilized with Ammonium Sulfate had significantly greater N₂O emissions than soils fertilized with Potassium Nitrate, even under high moisture content.
• The application of compost increased the pH of all soils (original pH of soils was lower than that of the compost).
• The main variables affecting N₂O emissions in this study were (from most important to least important): soil iron concentration, change in pH, native inorganic nitrogen, change in dissolved organic carbon and native dissolved organic carbon.

Recommendation:
The results indicate that to mitigate N2O emissions, compost applications should be avoided in high soil moisture conditions and when applied concurrently with Ammonium based fertilizers.